The 49-year-old, now in charge of Turkish giants Galatasaray, was shown the door at the Etihad Stadium towards the end of the 2012-13 season after City had relinquished the Premier League title they won 12 months earlier to arch-rivals Manchester United.
Mancini believes chairman Khaldoon Al Mubarak was heavily influenced by chief executive Ferran Soriano and director of football Txiki Begiristain when it came to dispensing with his services, and has since heard the wheels were in motion long before he left the hotseat.
He told The Sun on Sunday: "I know a lot of people in football and I found out afterwards that they were talking to three or four managers in February, March and April.
"I know they were talking to Pep Guardiola and Carlo Ancelotti.
"And these were the same people I was sat down with for dinner before the FA Cup final.
"It was like Judas. I trusted the chairman Khaldoon Al Mubarak 100 per cent, but not those other two guys. Probably he just followed them."
Mancini hit out at what he described as cowardly attitudes of the trio in dealing with his departure.
"Some people just don't have the courage to talk face to face," he added.
"Even Khaldoon did not tell me to my face what was happening.
"He could not just come up to me and say 'we did four years together, we won everything, we are happy, but now the job is finished'.
"Instead they were working behind my back and sacked me two games before the end of the season. I did not even have the chance to say goodbye to the Manchester City fans."